Drug delivery devices allowing for multiple dosing of a required dosage of a liquid medicinal product and further providing administration of such liquid drug to a patient, are as such well-known in the prior art. Generally, such devices have substantially the same purpose as that of an ordinary syringe.
Drug delivery devices of this kind have to meet a number of user specific requirements. For instance in case of those with diabetes, many users will be physically infirm and may also have impaired vision. Therefore, these devices need to be robust in construction, yet easy to use, both in terms of the manipulation of the parts and understanding by a user of its operation. Further, the dose setting must be easy and unambiguous and where the device is to be disposable rather than reusable, the device should be inexpensive to manufacture and easy to dispose. In order to meet these requirements, the number of parts and steps required to assemble the device and an overall number of material types the device is made from have to be kept to a minimum.
Typically, the medicament to be administered is provided in a cartridge having a moveable piston or bung mechanically interacting with a piston rod of a drive mechanism of the drug delivery device. By applying thrust to the piston in distal direction, a certain and pre-defined amount of the medicinal fluid is expelled from the cartridge.
Drug delivery devices, such as e.g. pen-type injectors, typically comprise a cartridge containing the medicament and a cartridge holder adapted to receive the cartridge and to serve as a mount for a replaceable needle assembly to be coupled with the inner volume of the cartridge in a fluid transferring way. For expelling a predefined dose of the medicament, the drug delivery device further comprises a drive mechanism having a piston rod to become operably engaged with the movable piston of the cartridge for exerting pressure to the piston in a distal direction.
The drive mechanism is typically mounted in a proximal housing section or in a body of the drug delivery device. In a final assembly, the cartridge holder and said body are interconnected. When generating or applying an injection force, a respective counterforce flows across at least two mechanical interfaces, e.g. from the drive mechanism to the body and from the body to the cartridge holder. However, each functional group and interface between functional groups of the drug delivery device inevitably introduce geometric tolerances to the mechanical force transmission system of such devices.
Prior to a first use of the device it most often necessary that the use conducts a setup procedure in order to ensure that the piston rod of the drive mechanism is in direct contact with piston of the cartridge. This setup step is necessary to ensure, that with a first injection procedure a correct and amount of the medicament is precisely dispensed.
Also, different medicaments and dosing instructions may require different device settings or usage of differently labelled drug delivery devices. Hence, there is a need to provide a large variety of drug delivery devices with different outer appearances.